Frequently Asked Questions

If you have any questions that aren't answered here, please contact us and ask!


Why can't I see printable puzzles?

Printable puzzles are in PDF format, so you need a PDF reader to view them. You can download the Adobe reader here:



Why underline pencil marks?

Underlining is used to make certain sets of pencil marks stand out. While you're free to use it however you like, it has special meaning for the "How Am I Doing?" checker, in that it marks a set of pencil marks as 'complete', where 'complete' means that you don't think any other values can possibly appear in the cell.

For example, imagine that you know there must be a 9 in one of two cells in a nonet, so you enter 9 as a pencil mark into both. They're the only pencil marks in those cells, as you haven't yet considered other numbers. If you were to use the "How Am I Doing?" checker at this point, it would be unreasonable for those cells to be highlighted as errors, given you haven't yet finished considering which other numbers they may contain. Underlining provides a way to indicate when you have finished considering which numbers a cell may contain.

How does the "How Am I Doing?" checker work?

The "How Am I Doing?" checker is used to check your progress. During the check, empty cells are ignored. Completed cells are checked directly against the solution and any incorrect values are marked as errors.

Pencil marks are checked only if they're underlined, as explained above. If the cell's correct value doesn't appear in the list of underlined pencil marks, the cell is marked as an error. If the pencil marks aren't underlined, they're assumed to be incomplete and are ignored.